Abstract
Fourier transform infrared (FTIR) spectroscopy was utilized to measure the long-wavelength optical lattice vibrations of high-quality quaternary A(x)ln(1-x-y)GaN thin films at room temperature. With AlN as buffer layers, the A(x)ln(1-x-y)GaN films were grown on c-plane (0001) sapphire substrates, using the plasma-assisted molecular beam epitaxy (PA-MBE) technique with aluminium (Al) mole fraction x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y = 0.1. The A(x)ln(1-x-y)GaN alloy exhibited two-mode behaviour, which includes A(1) (LO) and E-1 (TO).